Coinfection

CROI 2015: Sofosbuvir/Ledipasvir May Alter Antiretroviral Levels in HIV/HCV Coinfected People

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HIV/HCV coinfected people who take sofosbuvir/ledipasvir (Harvoni) to treat hepatitis C along with boosted protease inhibitor antiretroviral regimens may experience changes in drugs levels, but these are mostly not considered clinically relevant, according to a drug-drug interaction study presented at the 2015 Conference on Retroviruses and Opportunistic Infections (CROI) last month in Seattle. However, data on the safety and efficacy of combining sofosbuvir/ledipasvir and boosted protease inhibitors during treatment are lacking, and increased tenofovir exposure may be a concern.

The advent of interferon-free direct-acting antiviral regimens has brought about a revolution in treatment for chronic hepatitis C virus (HCV) infection, including for patients who have traditionally been considered "difficult to treat," such as those with HIV/HCV coinfection. Clinical trials have seen cure rates for coinfected people equal to those for patients with HCV alone, and current treatment guidelines and product labels indicate that HIV-positive patients can be treated with the same recommended regimens as HIV-negative ones, taking into account potential interactions with antiretroviral therapy (ART).

Polina German from Gilead Sciences reported findings from a Phase 1 study to evaluate interactions between sofosbuvir/ledipasvir and ART regimens containing ritonavir-boosted atazanavir (Reyataz) or darunavir (Prezista) plus tenofovir/emtricitabine (Truvada) in healthy HIV-negative volunteers.

Studies to date have shown that sofosbuvir and ledipasvir have limited potential for clinically significant drug-drug interactions, she noted as background. Sofosbuvir (but not its predominant metabolite GS-331007) and ledipasvir are substrates of P-glycoprotein (Pgp) and BCRP drug transporters, which play a role in drug distribution and elimination; ledipasvir also inhibits the action of Pgp and BCRP. However, neither sofosbuvir nor ledipasvir are metabolized by the cytochrome P450 enzymes that are inhibited by ritonavir -- which is how it raises levels of many medications including HIV protease inhibitors.

Before studying sofosbuvir/ledipasvir in HIV/HCV coinfected patients, Gilead scientists conducted drug-drug interaction studies with commonly used antiretroviral regimens. Early on, regimens containing efavirenz (Sustiva), raltegravir (Isentress), or rilpivirine (Edurant) plus Truvada were found to be safe when combined with sofosbuvir/ledipasvir; coinfected participants were limited to these ART regimens in  sofosbuvir/ledipasvir trials such as ION-4 and ERADICATE.

Co-administration with ritonavir-boosted HIV protease inhibitors is more challenging because ritonavir raises levels of many drugs. Sofosbuvir/ledipasvir did increase tenofovir levels somewhat in NNRTI-containing regimens due to its inhibition of Pgp and BCRP, but not enough to be considered clinically important. But tenofovir reaches higher levels when taken with ritonavir-boosted protease inhibitors, and when added to the effect of sofosbuvir/ledipasvir this could potentially bring levels high enough to cause kidney toxicity or other side effects.

German reported findings from a randomized, multiple-dose, cross-over study that included 97 participants without HIV or hepatitis C. About 70% were men, the mean age was 33 years, and whites, blacks, and Hispanics/Latinos were all well represented. 

In Part A, participants simultaneously received the fixed-dose sofosbuvir/ledipasvir coformulation (400mg/90mg) with either atazanavir/ritonavir (300mg/100mg) or darunavir/ritonavir (800mg/100mg) plus tenofovir/emtricitabine (300g/200mg) for 10 days. Based on the results of Part A, volunteers in Part B took sofosbuvir/ledipasvir and the antiretrovirals in a staggered fashion, separated by 12 hours, to see how this might change drug interactions.

The researchers measured plasma concentrations of sofosbuvir, its metabolite GS-331007, ledipasvir, and all the antiretrovirals over 24 hours and calculated pharmacokinetic (PK) parameters including overall, maximum, and minimum concentrations.

Results

The researchers stressed that there is currently no available data on the safety and efficacy of sofosbuvir/ledipasvir taken with boosted protease inhibitors in HIV/HCV coinfected patients. In their abstract they added that "the safety of higher tenofovir concentrations in this setting has not been established," and therefore "patients should be monitored for tenofovir-associated adverse reactions if co-administered."

German said that other on-going studies are evaluating sofosbuvir/ledipasvir with other antiretroviral regimens including dolutegravir (Tivicay) plus Truvada, and an investigational coformulation containing elvitegravir, cobicistat, emtricitabine and tenofovir alafenamide (TAF), a new version that has less of a detrimental effect on the kidneys and bones than the current tenofovir disoproxil fumarate (TDF).

3/10/15

Reference

P German, K Garrison, PS Pang, et al. Drug-Drug Interactions Between Anti-HCV Regimen Ledipasvir/Sofosbuvir and Antiretrovirals. 2015 Conference on Retroviruses and Opportunistic Infections. Seattle, February 23-24, 2015. Abstract 82.